Method for refining molten iron or molten iron alloys

ABSTRACT

METHOD FOR REFINING MOLTEN IRON OR MOLTEN IRON ALLOYS WHICH COMPRISES STEPS OF ADDING A REACTANT AND STIRRING THE UPPER LAYER PORTION OF SAID MOLTEN METAL WHILE BLOWING OXYGEN THEREONTO, AND SUBSTANTIAL INERTIA OF MOVEMENT AND NATURAL CONVECTION CAUSED BY POURING SAID MOLTEN METAL INTO THE LADLE BEING UTILIZED TO ENFORCE STIRRING EFFECT IN THE LADLE.

May 23, 1972 RYO ANDQ ETAL 3,664,827

METHOD FOR REFINING MOLTEN IRON OR MOLTEN IRON ALLOYS 2 Sheets-Sheet 1Filed April 22. 1969 May 23, 1972 RYOANDO ETAL 3,664,827

METHOD FOR REFINING MOLTEN IRON OR MOLTEN IRON ALLOYS Filed April 22.1969 2 Sheets-Sheet 2 PIC-3.2

United States Patent US. CI. 7551 3 Claims ABSTRACT OF THE DISCLOSUREMethod for refining molten iron or molten iron alloys which comprisessteps of adding a reactant and stirring the upper layer portion of saidmolten metal while blowing oxygen thereonto, and substantial inertia ofmovement and natural convection caused by pouring said molten metal intothe ladle being utilized to enforce stirring effect in the ladle.

BACKGROUND OF THE INVENTION This invention relates to a novel method andapparatus for refining molten iron or iron alloys and more particularyto a method and apparatus for rapidly removing impurities in molten pigiron, especially phosphorus and sulphur by causing it to react withoxygen and slag. Thus, this invention contemplates to readily removesuch impurities as phosphorus, sulphur and chromium and the like whilelimiting to the minimum the variation of other components, especiallycarbon, by mechanically stirring only the upper layer portion of molteniron kept in a ladle by means of a stirring rod made of carbonaceousmaterial or other refractory material while at the same time blowingoxygen onto the surface of the iron through a lance and by continuouslycharging a required quantity of reactant.

It is known that when refining molten pig iron with oxygen, the quantityof impurities generally decreases in the order of silicon and carbon,and that during the final stage of decarburization the quantity ofphosphorus, chromium, etc., decreases. Thus, with oxygen, it isimpossible to rapidly refine low phosphorus, high carbon steel. However,where a slag is prepared which is suitable to remove phosphorus andchromium at low temperature and the molten iron is caused to react withsuch a slag it is possible to remove phosphorus, chromium and the likein preference to decarburization. However, as shown by the followingequation, the dephosphorization reaction generally requires supply ofoxygen.

For example, to reduce the quantity of phosphorus from 0.2% to 0.05%,1.93 kg. (1.35 Nmfi) of oxygen per ton of molten metal pig iron isrequired. In order to perform rapid refining operation, it is desirableto blow oxygen in the form of pure oxygen or of air onto the surface ofthe molten pig iron through a lance. In this case, however, thetemperature of the surface portion of the molten iron with oxygen beingblown thereinto increases extremely, thus causing easy decarburization.Accordingly, in such a case, it has been known in the art to cause slag,which is advantageous for dephosphorization reaction, to contact withthe molten iron over as wide area as possible and over constantlyrenewed surface so as to enhance the movement of the molten iron toprevent excess rise in the temperature at the surface to which oxygen isblown and to bring the supplied oxygen into dephosphorization reactionas fast as possible.

ice

Based on these considerations the shaking ladle method, rotor method andthe like have been proposed. Further, in the steel manufacturingfurnace, soft blow refining with a L.D. converter has been practiced byutilizing a portion of above described considerations. Of these theshaking ladle method involves imparting eccentric motion to a containerof the molten pig iron or the ladle itself for the purpose of increasingthe speed of movement of the molten pig iron and to increase the contactsurface between the slag and the molten iron. Accordingly, splash of theslag and molten pig iron becomes excessive which requires an excessivelylarge container so that practical use of this method is limited.

The rotor method and the like do not result in rapid and sufficientdephosphorization. Moreover, any of these methods requires additionalprocess steps to the existing refining steps, so that they are diflicultto practice.

The soft blow refining process with a LD. converter requires a refiningtime twice as long as the ordinary refining time. In addition, even whenthe slag is sufficiently removed initially since a substantial quantityof slag remains adhered to the furnace body there is a problem thatphosphorus is again entrained in the iron during the finishing refiningstep.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a novel method and apparatus capable of removing impurities,especially phosphorus and sulphur from molten iron or iron alloyswithout the accompanying various diificulties described above.

According to this invention, use is made of a considerable inertia andconvection of the molten pig iron existing after pouring it into a ladleand the mechanical stirring is limited to the area receiving the blownoxygen and the area near the contact surface between the slag and themolten pig iron, or to only the upper layer portion of the molten pigiron. In addition, in order to minimize the splash, means are used tocreate a plurality of small stirring whirls or eddies. With thisinvention, even when a ladle is charged to about to of its normalcapacity, it is possible to perform a satisfactory refining operation sothat the invention is readily applicable to the existing molten irontransfer step. Briefly stated, the apparatus of this invention comprisesa mechanism for stirring the upper layer portion of the molten pig iron,a mechanism for blowing oxygen onto the surface of the molten pig iron,and a mechanism for charging a reactant into a ladle containing themolten pig iron.

BRIEF DESCRIPTION OF THE DRAWING Other features and objects of thisinvention, the mechanism and operation thereof can be more fullyunderstood from the following detailed description when taken inconjunction with the accompanying drawing in which:

FIG. 1 is a plan view of the apparatus embodying this invention, and;

FIG. 2 shows a vertical sectional view of the apparatus shown in FIG. 1in which the left hand half shows a section taken along a line Ila-Haand the right hand half shows a section taken along a line IIbHb in FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to theaccompanying drawing, a ladle for receiving molten pig iron and mountedon a suitable carriage is disposed substantially below the center of atreating table supporting frame 1. Stirring rods 3- of carbonaceousmaterial or other suitable refractory material are arranged in the upperportion of the ladle 2. Stirring rods 3 are secured to a disc 5 at thelower end of a stirring shaft 4 so that when the shaft 4 is lowered, the

stirring rods 3 are immersed into the upper portion of the molten pigiron kept in the ladle. The stirring shaft 4 is connected to a swingingframe 7 provided with three radial arms 6 and the vertical movement ofshaft 4 is effected by a motor 8 connected to the swinging frame 7through a. reduction gearing. At the lower side of the free end of eacharm 6 is projected a stub shaft 9. A shaft 11 driven through a suitabletransmission mechanism by a motor mounted on the treating tablesupporting frame 1 is provided thereon and the stub shafts 9 and theshaft 11 are interconnected with suitable eccentricity, for example, of150 mm. Accordingly, as the motor 10 is energized to drive the shaftthrough the transmission mechanism, the stub shaft 9 will be rotatedabout the axis of the shaft 11 with a radius corresponding to saideccentricity. In this manner, as the respective stub shafts 9 arerotated eccentically about the axis 11, the axis of stirring shaft 4Will be moved along a circle through arms 6 and the swinging frame 7,thus imparting a circular motion to stirring rods 3 to effect stirringof the surface of the molten pig iron.

The oxygen blowing mechanism comprises water cooled lances suspendedfrom a supporting structure 12 upstanding from the treating tablesupporting frame 1. The water cooled lances include a first lance 13which extends through a guide 14. First lance 13 is vertically moved bya suspension wire and is fixed to guide 14 by means of a handle 16. Asecond lance 13- which extends through a guide 14' secured to thestirring shaft 4, is vertically moved by a suspension wire 15 and issecured to the stirring shaft 4 by means of a handle 16'. In thisexample, the number of first lances 13 that are fixed to the treatingtable supporting frame is three whereas the number of second lances 13'secured to swinging shaft 4 is one. Oxygen is supplied to the treatingtable supporting frame 1 through a conduit 17, and distribution pipes 18branched from the conduit 17 are connected to lances 13 and 13' viaflexible pipes 19 to blow oxygen onto the upper surface of the moltenpig iron through the lower ends of lances 13- and 13'.

The reactant charging device includes a bucket 20 suspended from a hoist21 movable along a beam 22 on the treating table supporting frame 1. Thebucket 20 operated by the hoist 21 is used to supply the reactant into ahopper 23 mounted on the treating table supporting frame. At the bottomof the hopper 23 an electromagnetic feeder 24 is provided to incorporatethe reactant onto the surface of the molten pig iron in the ladlethrough a chute 25. Thus, proper adjustment of the electromagneticfeeder 24 assures positive and constant supply of the reactants.

As has been described hereinabove, this invention provides a refiningapparatus for molten iron comprising a stirring mechanism, an oxygenblowing mechanism and a reactant charging mechanism wherein oxygen isblown upon the surface of the molten pig iron through lances 13 and 13while the surface layer portion of the molten pig iron is stirred by theoperation of a motor 10* and wherein the reactant is continuouslycharged while the molten iron is stirred and the oxygen is blown.Accordingly, since only the surface layer portion is stirred, the powderrequired for this purpose may be relatively small particles, thusreducing the cost of installation. In addition, it is possible to blow alarge quantity of oxygen at high efliciencies. As the pressure ofblowing oxygen is low, the slag forming agent may be in the form ofsmall granules which not only increases the speed of forming the desiredslag but also enables readily adjustments of slag composition andtemperature. Further it is possible to employ existing ladles withoutthe necessity of changing the process steps.

Thus, this invention provides a novel method of refining iron and ironalloys which can readily and rapidly remove impurities therein andimprove the efficiency of oxygen and reactants so that ordinary pig ironfor cast iron and for steel manufacturing can be readily converted intopig iron of low phosphorus and sulphur content at very low cost. Thisalso enables manufacture with converters species of steel whichheretobefore could be obtained only with electric furnaces. Similarly,when pig iron of low phosphor and sulphur content or low silicon contentis prepared with electric furnaces, it becomes possible to charge alarge quantity of the pig iron into the electric furnace thus decreasingelectric power and hence cost of the raw material. Further it ispossible to increase the efiiciency of steel manufacturing and theuseful life of expensive refractories utilized in the furnace.

While the invention has been shown and described in terms of itspreferred embodiments, it will be clear to those skilled in the art thatmany alterations and modifications may be made within the true spiritand scope of the invention. For example, it is possible to refine ironby the method of the present invention either simultaneously with orafter desulphurization of pig iron. A plurality of lances for blowingoxygen may be provided aslant to the treating table supporting frame soas to blow oxygen from the upper corner of the ladle; and the locationof said lance is not limited to that herein defined-Le, in the axis ofstirring shaft.

The decrease of carbon in the molten iron is small in the presentrefining method because the main object of the invention lies in therefining of impurities, and not in the decarburization of major carboncontent.

What is claimed is:

1. In a method of refining molten iron or molten iron alloy wherein areactant is added thereto and the molten metal or alloy is stirred, theimprovement which comprises:

pouring said molten metal or alloy into a ladle,

adding a predetermined quantity of a reactant prox imate the surface ofsaid molten metal or alloy, and stirring only said molten metal or alloyproximate the surface thereof while thereonto blowing oxygen.

2. The method of refining molten iron or molten iron alloy according toclaim 1 wherein said reactant is added while there are substantialinertia of movement and natural convection caused by pouring said moltenmetal into said ladle.

3. The method of claim 1, wherein the molten metal is pig iron.

References Cited UNITED STATES PATENTS 2,110,066 3/1938 Heuer 55 X2,290,961 7/ 1942 Heuer 7555 X 2,397,737 4/ 1946 Heuer 7555 3,278,29510/1966 Ostberg 7561 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU,Assistant Examiner US. Cl. X.R. 7550,

